This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. I am writing to explore the possibility of initiating a collaboration to analyze the modifications of a Xenopus protein. My laboratory has been using cell-free extracts from Xenopus eggs to study the DNA damage response. One of our project is to evaluate the contribution of CtIP to double-strand break repair. We have set up a system to monitor DNA resection at DSBs and have shown in unpublished work that CtIP is critical for DNA resection. By performing depletion experiment followed by rescue with recombinant proteins, we have identified putative phosphorylation sites that influence CtIP activity. However, we don't know if or when these sites are phosphorylated. We have antibodies that quantitatively precipitate xCtIP and we want to assess CtIP phosphorylation (and potentially additional modifications) when the protein is bound to DNA, i.e. actively participating in DNA resection.